Repeater systems used in two-way radio communications enable users to communicate with a radio repeater which presumably is in an optimal location which acts to rebroadcast a message to one or more users around some coverage area. FIG. 1 is a prior art block diagram illustrating a single repeater system 100 where a subscriber 101 in a talkgroup A (TG A) presses the radio push-to-talk (PTT) and the repeater 103 receives a voice message from the subscriber 101 and transmits the message to all members of TG A, such as subscriber 105 and subscriber 107. Thus, in the single repeater system, those subscribers, such as subscriber 109 and subscriber 111, that are characterized as “polite” in other talk groups (e.g. TG B), will recognize that the channel is busy and do not transmit in order to prevent interference.
A peer-to-peer (P2P) radio system consists of two or more peers (repeaters) that are typically linked together over an internet protocol (IP) network where two or more subscriber two-way radio devices use the network to communicate over a greater range. Subscribers may participate in private calls, such as a one-to-one voice/data communication, or in group calls, such as a one-to-N voice/data communication where one subscriber is talking and N subscribers are listening. These subscriber stations require resources from peers in order to communicate with one other. For example, a subscriber can communicate with another subscriber co-located on the same peer (using the peer as an RF repeater), or with another subscriber on another peer. For voice communication in a dispatch system, short latency times in delivering the audio message is often a stringent requirement.
One problem in radio systems deals in situations where the number of subscribers that desire to transmit over one or more peers at the same time exceeds the number of available RF channels. In low cost P2P radio systems, the system may only have sufficient resources for one of the subscribers to transmit at one time. Although many subscribers may simultaneously be contending to communicate to other subscribers over the radio system, only one may transmit at a time on a given RF channel. Consequently, each of the peers will be responsible for determining which subscriber will be allowed to transmit. A subscriber which is transmitting using a given peer or peers is generally said to “have the floor” which gives the subscriber exclusive use to transmit to one or more other subscribers.
Thus, it would be advantageous to operate a low cost P2P communications system where a reliable means is used to arbitrate between contending subscribers that both require substantially simultaneous use of the floor.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.